An electric vehicle of this kind is disclosed, for example, in Japanese Patent Laid-Open Publication No. HEI-3-98404 entitled “Compact Electric Vehicle.” This electric vehicle includes an electric motor as a driving source and a deenergization-operating-type electromagnetic brake which releases the brake when being energized and applies the brake when not being energized. The electromagnetic brake releases the brake when an accelerator lever is operated, and applies the brake when the accelerator lever is not operated. Specifically, when the accelerator lever is in a neutral position, the electromagnetic brake is brought into a braking state.
For the operation of the electromagnetic brake based on information that the accelerator lever is in neutral, there are two methods of “immediately operating the electromagnetic brake” and “operating the electromagnetic brake after a lapse of a predetermined time period.”
The method of “immediately operating the electromagnetic brake” requires an electromagnetic brake which produces a large braking force in order to overcome an inertial force of the vehicle body. Thus increase in size and cost of the electromagnetic brake is inevitable. In the method of “operating the electromagnetic brake after a lapse of a predetermined time period,” the brake is operated after the inertial force of the vehicle body is reduced, which results in reduction in size and cost of the electromagnetic brake.
The vehicle, however, travels some distance due to inertia before the brake is operated, resulting in a long braking distance. In this context, it is desired to shorten the braking distance and reduce the cost of the electromagnetic brake in the electric vehicle.
Further, Japanese Patent Laid-Open Publication No. SHO-57-17650 discloses an “Electric Wheelchair” and Japanese Patent Laid-Open Publication No. 48-4260 discloses a “Controller for Direction and Propulsion of Electric Vehicle.”
The electric wheelchair of SHO-57-17650 includes left and right motors, left and right brake coils, left and right relays and left and right capacitors, being configured to control left and right driving wheels, respectively. More specifically, in the electric wheelchair, when an operating member is returned manually or automatically by the release of the control force to a neutral position, discharging of the left and right capacitors operates the left and right relays for a certain time, during which the motors are dynamically braked by use of resistors. When the operation of the left and right relays finishes in, e.g.,one minute, the mechanical brakes of the left and right brake coils work in addition to the dynamic brakes, stopping left and right drive shafts.
The above electric wheelchair, however, has the following problems (1) and (2).
(1) The left drive shaft is stopped by means of elements of the left capacitor, left relay, left resistor and left brake coil. The right drive shaft is stopped by means of elements of the right capacitor, right relay, right resistor and right brake coil. Between the left and right capacitors, left and right relays, and left and right brake coils, operational time differences exist, which are inevitable in electrical and mechanical operation. Further, between the left and right motors, an inevitable speed difference can exist. The accumulation thereof causes difference in stopping timing between the left drive shaft and the right drive shaft, resulting in the right or left turn of the electric wheelchair.
(2) In particular, when an operating element is turned to neutral during turning, the speed difference between the left and right motors results in an increased difference between the left and right stopping timings, substantially worsening riding comfort. Comfortable driving cannot thus be expected, and the countermeasure is required.
The same applies to the electric vehicle of SHO-48-4260.